Image forming method, image formng apparatus, intermediate transfer body, method of modifying surface of intermediate transfer body

ABSTRACT

The invention allows an image printing on a wide range of print media regardless of how much ink the print media absorb, without sacrificing a high printing flexibility of an ink jet printing system. To this end, the image forming method of this invention includes: a process of modifying a surface of an intermediate transfer body by applying energy to the surface; a process of ejecting ink onto the surface-modified intermediate transfer body by using an ink jet printing device; and a process of transferring ink from the intermediate transfer body to a print medium. With this invention, therefore, an ink image can be formed on the intermediate transfer body having a surface layer, without causing bleeding or beading, and then transferred onto the print medium in good condition.

TECHNICAL FIELD

The present invention relates to an image forming method and an imageforming apparatus both using an ink jet printing system, an intermediatetransfer body used in the image forming method and a method of modifyinga surface of the intermediate transfer body. More particularly thepresent invention relates to an image forming method and an imageforming apparatus, both of which use an intermediate transfer body informing an image on a print medium in order to make it unlikely for animage quality to be affected by the amount of ink absorbed in the printmedium, an intermediate transfer body used in the image forming methodand a method of modifying a surface of the intermediate transfer body.

BACKGROUND ART

A mainstream image forming method using paper as print media iscurrently an offset printing. The offset printing is a technique suitedfor mass printing. That is, a printing plate for an image is fabricatedand set in a printing machine to make copies of the image at a rate ofabout 9,000 copies per minute. Disadvantages of the offset printing,such as time and cost required by a printing plate production processand a vast investment needed to purchase the printing machine, havelittle adverse effect on the cost per printed sheet and speed becausethe printed matter is produced in large quantities. It can therefore besaid that the offset printing has matched market needs very well.

As a trend is gaining momentum in recent years for informationversatility and more and more diversified printed matters are printed insmall quantities, a problem has surfaced that the production cost ofprinting plates for individual printed matters becomes relatively high.Further, since instant availability of desired information is beinggiven greater importance, there is a growing demand for a shorterproduction period in which a printed matter becomes available. Since thecurrent offset printing has a long lead time, from a text preparation toa printing plate production and a printing familiarization (stabilizingof a printing machine), the production period cannot be shortened evenwhen the number of printed copies is small. Further, since a hugefacility investment is necessary and all processes require high levelsof skills, production locations are limited, which means it takes timefor printed matters to be delivered to customers.

In terms of meeting the market demands described above, the ink jetprinting system is drawing attention as a desirable technology. Sincethe ink jet printing system uses no printing plate, it is suited forprinting a small number of copies. Further, since it does not requirelarge-scale facilities or a high level of specialty knowledge, desiredprinted matters can be produced on demand and therefore growingexpectations are placed on the ink jet printing system.

Among points in which printed matters produced by the ink jet printingare inferior to offset-printed matters are a glossiness of printedmatter, a printability on thin paper, a printability on both sides ofpaper and a printing cost. If improvements are made on these points, theink jet printing system can be expected to advance toward commercialprinting.

The glossiness of printed matter is affected largely by a surfacesmoothness of paper (print medium). The ink jet printing system hasoften used a penetration type ink that permeates paper and fixes in it.Since a colorant of ink fixes following the surface of paper, the paperused needs to have a highly smooth surface to produce a glossiness.

Paper with a highly smooth surface generally has a low ink absorbingcapability. This is because a penetration type ink is absorbed through acapillary attraction. If printing is done on paper with a small inkabsorption capability, ink may remain on the surface without being fullyabsorbed in paper, which may cause undesired phenomena, such as ableeding in which the remaining ink becomes mixed with adjoining inkdroplets and a beading in which previously landed ink droplets are drawnto subsequently landed ink droplets, resulting in a degradation of aprinted image quality and a failure to dry properly. Under thesecircumstances, it is very difficult to form an image on paper with ahigh level of surface smoothness using the ink jet printing systemwithout causing these problems.

The ink jet printing system is available in two types: a continuous typeand an on-demand type, the latter type using electrothermal transducers(heating elements) and electromechanical transducers (piezoelectricelements). In either type only low-viscosity ink can be ejected. This isbecause the ink used in the ink jet printing system is required to behighly fluid while in the ink jet head to realize an adequate inkejection performance. At the same time, on the surface of the printmedium the ink is required to exhibit a low fluid characteristic toprevent adjoining ink droplets from getting mixed or from being drawn toeach other. In the ink jet printing system as described above, while ahighly fluid ink is ejected onto the print medium, the ink on the printmedium needs to have a low fluidity. That is, opposing characteristicsare required of the ink depending on whether it is in the print head oron the surface of the print medium.

To meet the contradictory requirements for the ink at the same time, anew system (an image forming system using an intermediate transfer body)is proposed in which an ink image is formed on a transfer body (or anintermediate transfer body), from which it is transferred onto a desiredprint medium to form the ink image on the print medium. In this systeman ink ejected from the ink jet head is affixed to the transfer bodytemporarily to form an ink image on the transfer body whose fluidity islowered to some extent while on the transfer body, and then the inkimage is transferred from the transfer body onto the print medium.

When such a transfer body is used, it is desired that the surface of thetransfer body be made a surface having a small ink absorbing capabilityor particularly a non-ink absorbing surface, considering an inktransferability from the transfer body to the print medium and an easewith which the transfer body can be cleaned after image transfer.However, if a transfer body with a non-ink absorbing surface is simplyused, an ink on the transfer body remains fluidized, making it difficultto hold an ink image on the transfer body in good condition. That is,the use of the non-ink absorbing surface as the intermediate transferbody surface to enhance the transferability of an ink image from theintermediate transfer body makes it difficult to hold the ink image onthe intermediate transfer body in good condition. Conversely, if thesurface of the transfer body is made a surface that has a high inkabsorbing capability to enhance the ability to hold the ink image on theintermediate transfer body, it becomes difficult to keep a goodtransferability of the ink image from the intermediate transfer body.

In the image forming system using the intermediate transfer body asdescribed above, it is important in keeping a high quality of an inkimage on the print medium to strike a good balance between a high levelof capability to hold an ink image on the intermediate transfer body anda high level of transferability of the ink image from the intermediatetransfer body. However, an image forming system has yet to be realizedwhich establishes both a high level of capability to hold an ink imageon the intermediate transfer body and a high level of transferability ofthe ink image from the intermediate transfer body and which can form ahigh quality of ink image on a variety of kinds of print media.

In Japanese Patent Application Laid-open No. 5-330035 (1993), forexample, a method is proposed in which a transfer body is heated toincrease a density of ink on the transfer body and thereby lower an inkfluidity on the transfer body. Simply heating the transfer body,however, can lower the ink fluidity only to a small extent, resulting inan ink image instantly spreading on the transfer body. That is, the inkimage cannot be held in good condition on the transfer body, which inturn renders the ink image on a print medium after transferunsatisfactory. This method has a problem that heat of the transfer bodymay reach an ink jet head and dry ink ejection nozzles, causing ejectionfailures. This method therefore has not yet been put to practical use.

Another method has been proposed which, as in Japanese PatentApplication Laid-open No. 7-223312 (1995), uses a hot-melt ink and heatsan ink jet head and an ink supply system to eject the melted hot-meltink. In this case, however, since a thickness of affixed ink is large,an ink image formed on the print medium after transfer looks unnatural,making the quality of the image on the print medium after transfer lessthan satisfactory, similar to the method disclosed in Japanese PatentApplication Laid-open No. 5-330035 (1993). When the hot-melt ink isused, the ink needs to be heated to a desired melted state. This meltingprocess takes time and there are some limitations on the components ofink, leaving much to be desired.

DISCLOSURE OF THE INVENTION

As can be seen from the above, in the ink jet printing system the use ofan intermediate transfer body is advantageous in enhancing a level offreedom in the selection of print media. However, even the systememploying the intermediate transfer body still has room for improvementto make a transferred ink image on the print medium high in quality.

One of important tasks that need to be addressed, in particular, is tocope with two contradicting requirements, i.e., a high ink imageretainability on the intermediate transfer body and a high ink imagetransferability from the intermediate transfer body to a print medium,to make the transferred ink image on the print medium a quality image.

The present invention has been accomplished with a view to overcomingthe above problem. It is therefore an object of this invention toprovide an image forming method and an image forming apparatus which canprovide a unique combination of a high ink image retainability on anintermediate transfer body and a high ink image transferability from theintermediate transfer body to a print medium in order to allow a highquality image printing on a wide range of print media regardless of howmuch ink the print media absorb, without sacrificing the high printingflexibility of the ink jet printing system. It is another object of thisinvention to provide an intermediate transfer body used in the imageforming method and also a method of modifying a surface of theintermediate transfer body.

More specifically, this invention makes it possible to form an image onthe intermediate transfer body having a surface layer with goodreleasability, without causing bleeding or beading, and then to transferthe ink removed of water from the intermediate transfer body to theprint medium in good condition.

In a first aspect of the present invention, there is provided an imageforming method comprising the steps of:

performing surface-modifying processing on a surface of an intermediatetransfer body by applying energy to the surface;

forming an image on the surface-modified intermediate transfer body byejecting ink from an ink jet printing means; and

transferring the image formed on the intermediate transfer body onto aprint medium.

In a second aspect of the present invention, there is provided an imageforming method comprising the steps of:

providing an intermediate transfer body having a surface containing atleast one of a fluorine compound and a silicone compound, and beingsurface-modified through plasma processing for modification of thesurface;

forming an image on the intermediate transfer body by ejecting ink froman ink jet printing means; and

transferring the image formed on the intermediate transfer body onto aprint medium.

In a third aspect of the present invention, there is provided an imageforming apparatus comprising:

means for mounting an intermediate transfer body being surface-modifiedthrough application of energy for modification of the surface;

means for forming an image on the intermediate transfer body mounted onthe mounting means by ejecting ink from an ink jet printing means; and

means for transferring the image formed on the intermediate transferbody onto a print medium.

In a fourth aspect of the present invention, there is provided an imageforming apparatus comprising:

means for mounting an intermediate transfer body having a surfacecontaining at least one of a fluorine compound and a silicone compound,and being surface-modified through plasma processing for modification ofthe surface;

means for forming an image on the intermediate transfer body mounted onthe mounting means by ejecting ink from an ink jet printing means; and

means for transferring the image formed on the intermediate transferbody onto a print medium.

In a fifth aspect of the present invention, there is provided an imageforming method using an intermediate transfer body beingsurface-modified through application of energy for modification of thesurface, the method comprising the steps of:

applying a first liquid for increasing an ink viscosity to theintermediate transfer body;

forming an image by ejecting ink from an ink jet printing means onto theintermediate transfer body already applied with the first liquid; and

transferring the image formed on the intermediate transfer body onto aprint medium.

In a sixth aspect of the present invention, there is provided an imageforming apparatus method comprising the steps of:

providing an intermediate transfer body having a surface containing atleast one of a fluorine compound and a silicone compound, and beingsurface-modified through plasma processing for modification of thesurface;

applying a first liquid for increasing an ink viscosity to theintermediate transfer body;

forming an image by ejecting ink from an ink jet printing means onto theintermediate transfer body already applied with the first liquid; and

transferring the image formed on the intermediate transfer body onto aprint medium.

In a seventh aspect of the present invention, there is provided asurface-modifying method of an intermediate transfer body comprising astep of surface-modifying through application of energy, theintermediate transfer body being used for forming an image formed of inkonto the surface, and for transferring the image formed on the surfaceonto a print medium.

In an eighth aspect of the present invention, there is provided asurface-modifying method of an intermediate transfer body comprising thesteps of:

providing an intermediate transfer body having a surface containing atleast one of a fluorine compound and a silicone compound, and being usedfor forming an image formed of ink onto the surface, and fortransferring the image formed on the surface onto a print medium, and;

surface-modifying the provided intermediate transfer body throughapplication of energy for modification of the surface.

In a ninth aspect of the present invention, there is provided anintermediate transfer body being surface-modified through application ofenergy, and being used for forming an image formed of ink onto thesurface, and for transferring the image formed on the surface onto aprint medium.

In a tenth aspect of the present invention, there is provided anintermediate transfer body having a surface containing at least one of afluorine compound and a silicone compound, being surface-modifiedthrough plasma processing for modification of the surface, and beingused for forming an image formed of ink onto the surface, and fortransferring the image formed on the surface onto a print medium.

In an eleventh aspect of the present invention, there is provided animage forming method comprising the steps of:

performing surface-modifying processing on a surface of an intermediatetransfer body through plasma processing and surfactant application, thesurface containing at least one of a fluorine compound and a siliconecompound;

forming an image on the surface-modified intermediate transfer body byejecting ink; and

transferring the image formed on the intermediate transfer body onto aprint medium.

In a twelfth aspect of the present invention, there is provided an imageforming method comprising the steps of:

providing an intermediate transfer body having a surface containing atleast one of a fluorine compound and a silicone compound, and beingsurface-modified through plasma processing and application of asurfactant for modification of the surface;

forming an image on the surface-modified intermediate transfer body byejecting ink from an ink jet printing means; and

transferring the image formed on the intermediate transfer body onto aprint medium.

In a thirteenth aspect of the present invention, there is provided animage forming apparatus using an intermediate transfer body having asurface containing at least one of a fluorine compound and a siliconecompound, the apparatus comprising:

means for surface-modifying processing on the intermediate transfer bodythrough plasma processing and surfactant application,

means for forming an image on the surface-modified intermediate transferbody by ejecting ink; and

means for transferring the image formed on the intermediate transferbody onto a print medium.

In a fourteenth aspect of the present invention, there is provided animage forming apparatus comprising:

means for mounting an intermediate transfer body having a surfacecontaining at least one of a fluorine compound and a silicone compound,and being surface-modified through plasma processing and surfactantapplication for modification of the surface;

means for forming an image on the intermediate transfer body mounted onthe mounting means by ejecting ink from an ink jet printing means; and

means for transferring the image formed on the intermediate transferbody onto a print medium.

In a fifteenth aspect of the present invention, there is provided animage forming method comprising the steps of:

subjecting a surface of an intermediate transfer body to plasmaprocessing;

applying a liquid onto the intermediate transfer body after plasmaprocessing, the liquid containing a surfactant for improving awettability of the surface of the intermediate transfer body;

applying a reactant liquid for reacting to ink onto the intermediatetransfer body to which the liquid containing the surfactant was applied;

forming an image on the intermediate transfer body after application ofthe reactant liquid by ejecting ink from an ink jet printing means; and

transferring the image formed on the intermediate transfer body onto aprint medium.

In a sixteenth aspect of the present invention, there is provided animage forming method comprising the steps of:

providing an intermediate transfer body having a surface containing atleast one of a fluorine compound and a silicone compound, and beingsurface-modified through plasma processing and application of a liquidcontaining a surfactant for modification of the surface;

applying a liquid onto the intermediate transfer body after plasmaprocessing, the liquid reducing the fluidity of an ink on theintermediate transfer body;

forming an image on the intermediate transfer body after application ofthe liquid by ejecting ink from an ink jet printing means; and

transferring the image formed on the intermediate transfer body onto aprint medium.

In this specification, “print medium” refers not only to paper commonlyused in printing devices but also widely to cloth, plastic films and anyother material capable of receiving ink.

An ink jet printing means applicable to this invention includes avariety of types of ink jet heads proposed for ink jet printing, such asone that utilizes thermal energy generated by electrothermal transducersto cause film boiling in ink and thereby form bubbles to eject ink, onethat uses electromechanical transducers to eject ink, and one thatutilizes static electricity or air flow to eject ink droplets. Of these,the electrothermal transducer-based ink jet head is advantageously usedfrom the standpoint of size reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an outline configuration of animage forming apparatus according to one embodiment of this invention;

FIG. 2 is a block diagram showing an example control system constructedto control the image forming apparatus of FIG. 1;

FIG. 3 is a flow chart showing an example sequence of image formingprocessing using the control system of FIG. 2;

FIG. 4 is a flow chart showing an example sequence of image formingprocessing according to a second embodiment of this invention; and

FIG. 5 is a flow chart showing an essential part of the sequence ofimage forming processing according to the second embodiment of thisinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Example embodiments of the present invention will be described in detailby referring to the accompanying drawings.

I. First Embodiment

1. Outline of Image Forming Device

FIG. 1 is a schematic diagram showing an outline configuration of animage forming apparatus according to one embodiment of this invention.In FIG. 1, reference number 1 denotes an intermediate transfer bodywhich is driven to rotate about an axis 1A in a direction of arrow F andhas a surface layer 2 with good releasability. In FIG. 1, referencenumber 3 represents an energy application device that performs surfacemodifying processing on the surface layer 2. In the device shown in FIG.1, application devices 4, 5 are put in contact with the surface of theintermediate transfer body 1 between the energy application device 3 andan ink jet printing unit 6 to apply a wettability improvement componentand an ink viscosity increasing component to the surface. Although theapplication device 4 for applying a wettability improvement componentsuch as surface active agent and the application device 5 for applyingan ink viscosity increasing component do not have to be provided, theyare preferably installed from a standpoint of improving the capabilityof the intermediate transfer body to hold an ink image.

After these components have been applied to the surface, the ink jetprinting unit 6 ejects ink droplets onto the surface of the intermediatetransfer body 1 to form an image (mirror image) on the surface. Then, aprint surface of a print medium 10 is brought into contact with theimage formed on the intermediate transfer body 1 and a pressure roller11 is pressed against a back of the print medium 10 to transfer theimage onto the print medium 10.

In the device shown in FIG. 1, a water removal facilitating device 8 isprovided in the form of a fan to evaporate and remove water or solventcomponents from the ink that forms the image on the intermediatetransfer body 1. In addition to or in place of this arrangement, a heatroller 9 may be used which is placed in contact with a back side of thehollow intermediate transfer body 1.

The print medium 10, after being printed with an image through theintermediate transfer body 1 as described above, is pressurized betweenfixing rollers 12 to have an excellent surface smoothness. It is alsopossible to heat the print medium 10 with the fixing rollers 12 toinstantly give the printed material a durability.

Then, in the device of FIG. 1, after having transferred the ink image tothe print medium 10, the intermediate transfer body is washed by acleaning unit 13 at the next stage in preparation for receiving the nextimage.

In the conventional ink jet printing system, ink fixing is mostlyachieved by the penetrating of ink into paper as the print medium andthe state of image formed varies depending on the amount of ink absorbedin the print medium. So, there are limitations on the kinds of printmedia that can be used. The offset printing device on the other hand,because it is designed for mass printing of the same printed matter,lacks flexibility as when producing different image outputs on differentpages.

With the present invention, however, the following advantages areproduced. As can be seen from the above-described image formingapparatus embodying this invention, the kinds of print media are notlimited by the amount of ink absorbed in the print medium, allowing ahigh quality printing on a wide range of media. This in turn realizes animage forming that takes advantage of the features of the ink jetprinting system, such as an excellent flexibility of being able toinstantly produce a desired printed matter.

2. Description of Processes

The image forming apparatus described above includes means to perform aprocess of modifying the surface of the intermediate transfer body 1having a surface layer with good releasability through energyapplication (hereinafter referred to as a process (X)), a process offorming an image by the ink jet printing system on an intermediatetransfer body having the modified surface (process (Y)), and a processof transferring the ink image formed on the intermediate transfer body 1onto a print medium (process (Z)). These processes (X)-(Z) and the meansfor implementing them will be explained by way of example.

2.1 Process (X)

The process (X) modifies the surface of the intermediate transfer body 1having a surface layer with good releasability by energy application.

In the embodiment of FIG. 1, a drum made of light metal such as aluminumalloy is used as a support for the surface layer of the intermediatetransfer body, considering characteristic requirements including astiffness to withstand a pressure applied during a transfer process, adimensional accuracy and a control responsivity that can be improvedthrough a reduction in rotary inertia. On the drum surface is providedthe surface layer 2, thus forming the intermediate transfer body 1.

The intermediate transfer body or the support for its surface layer,however, is only required to ensure that the surface layer can at leastbe in line contact with the print medium. Depending on the configurationof the image forming apparatus or the form of transfer onto the printmedium; they may be formed into a shape of roller, belt or sheet. Inaddition to the materials that assure the line contact, the intermediatetransfer body may also use materials with large elastic deformations,such as a pad which is used in a pad printing.

As shown in FIG. 1, on the surface of the intermediate transfer body 1is formed the surface layer 2 with good releasability. In thisspecification, the good releasability means a state in which an inkimage can be removed without adhering to the surface of the intermediatetransfer body. The higher the releasability, the more advantageous thesurface layer 2 is in terms of a load during cleaning and an inktransfer rate. On the contrary, as the releasability increases, acritical surface tension of a material generally decreases, making thematerial more likely to repel a liquid such as ink, which in turnrenders the ink image more difficult to retain on the surface layer. Amaterial preferably used in this invention exhibits a physical propertybefore surface treatment such that its water repellency is 30 mN/m orless in critical surface tension or 70 degrees or more in contact anglewith water. That is, the preferred material for the intermediatetransfer body of this invention has a property such that theintermediate transfer body, before being surface treated, repels appliedink which therefore fails to form an image (i.e., the ink imageretention capability is low) as long as ordinary means is used.

More specifically, the surface layer 2 with good releasability may beformed by performing surface treatments, such as coating fluorine on thesurface of the intermediate transfer body or applying silicone oil tothe surface. However, it is desired that the surface layer 2 is formedof an elastic material with good releasability because it can achieve ahigher transfer efficiency. The elastic material may advantageously usesurface-treated NBR and urethane rubber and also fluororubber andsilicone rubber both inherently having good releasability. Siliconerubber is available in various types, such as vulcanization type,one-liquid curing type and two-liquid curing type. All of these typescan be used properly. Although a hardness of the elastic rubber of thesurface layer depends on the thickness and stiffness of the print medium10 in contact with the surface layer and thus it is desirable tooptimize the surface layer hardness, the use of the elastic rubber ofwith a hardness of between 10 and 100 degrees when measured by type Adurometer (conforming to JIS K 6253) produces a desirable effect. Almostall kinds of print media can be dealt with if the elastic rubber has ahardness of between 40 and 80 degrees.

In the process (X) the surface layer 2 of the intermediate transfer body1 constructed as described above is modified by applying energy to it.The application of energy to the surface of the intermediate transferbody improves a wettability of the surface of the material that has agood releasability, thereby suppressing an ink repellency. The surfaceof the intermediate transfer body thus obtained has a good imageretention capability (an ability to hold ink droplets where they land byproperly suppressing the ink repellency) in addition to good cleaningand image transferring capabilities. The means for energy applicationmay be any means that can modify the surface to make it hydrophilic byperforming surface treatment, such as ultraviolet radiation,flame-treatment, corona discharging and plasma treatment. Of these,plasma treatment at an atmosphere pressure or reduced pressure is apreferred method which is particularly advantageous if the surface layerwith good releasability is formed of a material containing a fluorinecompound or silicone compound. Not only can this combination provide anefficient hydrophilic surface treatment but it can also prevent thetransfer rate from falling or improve the transfer rate whentransferring an ink image formed on the intermediate transfer body ontoa print medium in a later process. The plasma treatment mentioned aboveincludes a part of the corona discharge treatment which activates oxygenin atmosphere to produce hydroxyl groups on the surface of a substratebeing processed. The fluorine compound or silicone compound includesrespective oil component.

A complete mechanism behind the desirable effect produced by thecombination of the selected material and the selected surfacemodification means has yet to be revealed. However, there seems to be aremarkable tendency that, in the presence of fluorine or silicone oilcomponent, both the hydrophilic surface and the maintained or improvedtransfer rate are clearly observed simultaneously and that the surface,once modified, can retain these lasting effects. Judging from thesefacts, it is assumed that, in addition to the generally known chemicalaction of the plasma treatment (introduction of hydrophilic groups onthe surface) which makes hydrophilic at least a part of the rubbercomponent, filler component and oil component of the surface layer, aphysical action (surface roughening) changes a part of a rubberstructure to promote the oil component movement on the surface.

The surface treatment may be implemented as shown in the embodiment ofFIG. 1, in which an energy application device 3 modifies the surface ofthe intermediate transfer body 1 with good releasability continuously orat predetermined intervals. Alternatively the surface treatment may alsobe performed by not using the energy application device 3 and by usingan intermediate transfer body which has its surface modified in advance.These two methods may be combined, i.e., it is possible to use anintermediate transfer body with its surface already modified and performadditional surface modification treatments on the surface layer 2 atappropriate intervals by using the energy application device 3 installedin the system to maximize the surface modification effect according tothe number of sheets printed.

2.2 Process (Y)

This is a process of forming an image on the intermediate transfer bodyby using an ink jet printing unit.

The ink jet printing unit used for image forming is not limited in termsof the ink ejection mode and configuration. The ink jet printing unitmay be one that performs ink ejection in a continuous mode or in anon-demand mode using electrothermal transducers (heating elements) orelectromechanical transducers (piezoelectric elements). As to theconfiguration of the ink jet printing unit, let us look at theconstruction of FIG. 1, for example. An ink jet head may be of a linehead configuration in which ink ejection nozzles are arrayed in an axialdirection of the intermediate transfer body 1 (in a directionperpendicular to the plane of the drawing). Another type of head may beused which has its nozzles arrayed over a predetermined range in adirection of a tangential line or in a circumferential direction of theintermediate transfer body. Printing is done by scanning this head inthe axial direction. Further, it is possible to use the same number ofprint heads as that of the ink colors used in forming an image.

Inks used in the image forming process (Y) are also not subject to anyparticular limitations. It is possible to use commonly available dyesand pigments as colorants of ink and also use water-based inks that haveaqueous liquid medium to dissolve and/or disperse dyes and pigments.Pigment inks are particularly suitable for producing a durable printedimage.

Among possible dyes are C.I. Direct Blue 6, 8, 22, 34, 70, 71, 76, 78,86, 142, 199, C.I. Acid Blue 9, 22, 40, 59, 93, 102, 104, 117, 120, 167,229, C.I. Direct Red 1, 4, 17, 28, 83, 227, C.I. Acid Red 1, 4, 8, 13,14, 15, 18, 21, 26, 35, 37, 249, 257, 289, C.I. Direct Yellow 12, 24,26, 86, 98, 132, 142, C.I. Acid Yellow 1, 3, 4, 7, 11, 12, 13, 14, 19,23, 25, 34, 44, 71, C.I. Food Black 1, 2, and C.I. Acid Black 2, 7, 24,26, 31, 52, 112, 118.

Among possible pigments are C.I. Pigment Blue 1, 2, 3, 15; 3, 16, 22,C.I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 112, 122, C.I.Pigment Yellow 1, 2, 3, 13, 16, 83, Carbon Black No. 2300, 900, 33, 40,52, MA 7, 8, MCF 88 (Mitsubishi Kasei make), RAVEN1255 (Columbia make),REGAL330R, 660R, MOGUL (Cabot make), Color Black FW1, FW18, S170, S150,and Printex35 (Degussa make).

These pigments are free from any limitations in terms of applicationmode. They can be used in the form of, for instance, self dispersiontype (pigment free of dispersant), resin dispersion type andmicrocapsule type. Suitable pigment dispersions include a water-solubledispersion resin with a weight-averaged molecular weight of about 1,000to 15,000. More specifically, they include water-soluble vinyl resin,block or random copolymers and salts thereof made from styrene and itsderivatives, vinylnaphthalene and its derivatives, aliphatic alcoholesters of α,β-ethylenically-unsaturated carboxylic acid, acrylic acidand its derivatives, maleic acid and its derivatives, itaconic acid andits derivatives, or fumaric acid and its derivatives.

To improve the durability of the image formed, a water-soluble resin anda water-soluble cross-linking agent may be added. The only requirementfor these materials is that they can coexist with ink components. As thewater-soluble resin, the above-mentioned dispersion resins may besuitably used. As the water-soluble cross-linking agent, oxazoline andcarbodiimide, which have slow responsivity, may be suitably used interms of ink stability.

The aqueous liquid medium making up the ink along with the colorantslisted above may contain an organic solvent, and the amount of organicsolvent is a determining factor of the property of the ink after itsviscosity is raised. In the system using an intermediate transfer bodyaccording to this invention, the ink when it is transferred onto theprint medium contains almost only the colorant and a high boiling pointorganic solvent. Considering this fact, the amount of organic solvent isdetermined at its optimum value. Preferred organic solvents include thefollowing water-soluble materials with a high boiling point and a lowvapor pressure.

The organic solvents may include, for example, polyethylene glycol,polypropylene glycol, ethylene glycol, propylene glycol, butyleneglycol, triethylene glycol, thiodiglycol, hexylene glycol, diethyleneglycol, ethylene glycol monomethyl ether, diethylene glycol monomethylether or glycerin. Two or more of these may be mixed for use. To adjustviscosity and surface tension, alcohols such as ethyl alcohol andisopropyl alcohol or surface active agents may be added to ink.

As for a compounding ratio of components making up the ink, there is nolimitation. The compounding ratio can be adjusted properly according tothe chosen ejection force and nozzle diameters of the ink jet head. Theink may, for example, be composed of 0.1-10% colorant, 5-40% solvent,0.01-5% surface active agent and the remaining percentage of purifiedwater.

When an image forming is done at high speed, it is effective to providea process of applying an ink viscosity increasing component to theintermediate transfer body prior to the ink ejection process (Y). Theink viscosity increasing component not only suppresses the fluidity ofink on the intermediate transfer body to minimize bleeding and beadingduring the high-speed image forming but also improves the capability ofretaining an ink image on the intermediate transfer body.

That is, since, during the fast image forming, the amount of ink appliedper unit time is greater than normal, bleeding and beading are morelikely to occur. On the intermediate transfer body the ink is alsolikely to become fluidized. Thus, when the device of FIG. 1 is used, theink viscosity increasing component is applied by the application device5 prior to ink application so that the ink droplets will land where theink viscosity increasing component has been applied. This arrangementensures that the ink and the ink viscosity increasing component comeinto contact with each other at positions where the ink droplets havelanded, reducing the fluidity of the ink and thereby holding the inkwhere it landed.

Here, an increase in ink viscosity includes not only a case in whichcolorants and resins making up the composition of ink contact the inkviscosity increasing component to cause a chemical reaction or aphysical adsorption, resulting in an overall rise in ink viscosity, butalso a case in which solid components of the ink composition coagulate,resulting in a local rise in ink viscosity.

The usable ink viscosity increasing component should properly be chosenaccording to the kind of ink used for image forming. For a dye ink, forinstance, it is effective to use a high molecular coagulant. For apigment ink having fine dispersed particles, a liquid containing metalions attributable to coagulation of pigment is advantageously used.Further, if the dye ink as the ink and metal ions as the ink viscosityincreasing component are used, it is preferred that a pigment componentof an identical color with that of the dye component be mixed into theink, that white or transparent fine particles which have little effectson the color be added, or that a water-soluble resin which reacts withmetal ions be added.

The high molecular coagulants used as the ink viscosity increasingcomponent include, for example, cationic high molecular coagulants,anionic high molecular coagulants, nonionic high molecular coagulantsand amphoteric high molecular coagulants. Metal ions include, forexample, divalent metal ions such as Ca²⁺, Cu²⁺, Ni²⁺, Mg²⁺ and Zn²⁺,and trivalent metal ions such as Fe³⁺ and Al³⁺. If a liquid containingthese metal ions is applied, it is preferably applied in the form of ametal salt solution in water. Among anions of metal salts are Cl⁻, NO₃⁻, SO₄ ²⁻, I⁻, Br⁻, ClO₃ ⁻ and RCOO⁻ (R represents an alkyl group).

The amount of ink viscosity increasing component to be applied ispreferably set such that the total number of metal ion charges is equalto or more than 0.5-2 times the total number of ion charges of oppositepolarity present in the colored ink. For this purpose, a water solutionof the metal salts listed above with a density of about 10% by mass maybe used. This layer of ink viscosity increasing component, even if thin,can achieve its desired function well.

While FIG. 1 shows the application device 5 of a roll coater type as apreferred application means, other types of application means may alsobe used, such as a spray coater. It is also possible to use a print headthat ejects a liquid of viscosity increasing component by the action ofthe ink jet mechanism.

For improving the durability of a finally formed image, a water-solubleresin and a water-soluble cross-linking agent may be added. There is nolimitation on these materials as long as they can coexist with the inkviscosity increasing component. If metal salts with high reactivity areused as the ink viscosity increasing component, the water-soluble resinmay advantageously use PVA and PVP. The water-soluble cross-linkingagent may preferably use oxazoline and carbodiimide that reactscarboxylic acid suitably used in ink for colorant dispersion. Aziridinein particular is the material that can provide a combination of an inkviscosity increasing capability and an improved image durability.

For uniform application of the ink viscosity increasing component, it iseffective to add a surface active agent or surfactant to the inkviscosity increasing component or, before applying the ink viscosityincreasing component, to coat a wettability improving component such asa surfactant to the intermediate transfer body by the application device4. The wettability improving component is designed to increase anaffinity between the intermediate transfer body and the ink viscosityincreasing component and therefore preferably uses a surfactant.

Even in a configuration that does not use the ink viscosity increasingcomponent, the application of the wettability improving component suchas a surfactant by the application device 4 prior to ink ejection iseffective in improving the affinity of the intermediate transfer bodywith ink.

In forming an image, if the coated layer of the ink viscosity increasingcomponent is thin, there is no problem normally. There are cases,however, in which a better printed result can be obtained by drying wellthe ink viscosity increasing component after its application by a dryingprocess before ejecting ink. In that case, a drying means may beprovided between the application device 5 and the ink jet printing unit6.

2.3 Process (Z)

This is a process of transferring an ink image formed on theintermediate transfer body 1 onto the print medium 10 which can take aform of continuous paper, such as roll paper and fanfold paper, inaddition to cut-sheet paper. The print medium 10 is brought into contactwith the image forming surface of the intermediate transfer body 1 bythe pressure roller 11 and thereby receives ink. In this embodiment,since at this stage the water in the ink on the intermediate transferbody 1 has already evaporated to some degree and its viscosity hasrisen, a good quality image can be formed on a print medium even if ithas a small ink absorbing capacity.

If, however, the time from the ink image forming in the process (Y) tothe image transfer in the process (Z) is too short, the amount of watercontained in ink may not decrease by natural evaporation to a levelallowed by the print medium. Taking such a case into consideration, theimage forming apparatus of FIG. 1 has the water removal facilitatingdevice 8 in the form of a fan (which may send warm air) installedbetween a position where an ink image is formed and a position where animage transfer is performed, thereby promoting water elimination fromink. Another means for facilitating the water removal may be one whichheats the intermediate transfer body from the ink image forming surfaceside. Alternatively, it may be realized by a heat roller 9 put incontact with the back side of the hollow intermediate transfer body 1 toheat the surface of the intermediate transfer body.

The print medium printed through the intermediate transfer body asdescribed above is pressurized by the fixing rollers 12 to have anexcellent surface smoothness. The fixing rollers 12 may also be providedwith a function of heating the print medium 10. This will instantly givethe printed material a durability.

In the device exemplified in FIG. 1, the intermediate transfer body,after having transferred an ink image to the print medium, is thenwashed by the cleaning unit 13 installed in the next stage inpreparation for receiving the next image. The cleaning means preferablyemploys a direct cleaning method or a wiping method. The direct cleaningmethod may involve washing or wiping while spraying water shower orputting the intermediate transfer body surface in contact with watersurface. The wiping method may involve holding a wet morton rolleragainst the surface. These two methods may of course be used incombination.

After washing, if necessary, the surface of the intermediate transferbody may be pressed by a dry morton roller or applied air blow foreffective drying. Depending on the ink used, the component compoundedfor the purpose of improving the wettability may be utilized forcleaning. In that case, the wettability improving component applicationdevice 4 may also be used as the cleaning means.

2.4 Advantages of Embodiment

The above processes and the means to implement them have been describedin detail. The feature of this invention and embodiment can besummarized as having established a technology that can modify a surfaceof intermediate transfer body having a high transferability, forinstance, having a good releasability, into a surface capable ofreceiving an ink or an ink viscosity increasing component withoutrepelling them. This technology provides a unique combination of a highperformance in transferring an ink image from the intermediate transferbody to a print medium and a high capability in holding an ink image onthe intermediate transfer body, making the quality of the transferredink image on the print medium high. Why this is possible will beexplained in detail.

The reason that the surface of the intermediate transfer body 1 is givena good releasability is to improve an ink transfer efficiency. Withgeneral transfer means including an offset printing, only about half theink on the surface of the intermediate transfer body is transferred ontothe print medium with the remaining half left on the intermediatetransfer body. The intermediate transfer body with the residual ink onits surface then receives the next ink supply. In other words, thesurface of the intermediate transfer body needs to be supplied two timesthe amount of ink required on the print medium. If the transferefficiency is improved, the amount of ink to be supplied to theintermediate transfer body can be reduced. With this invention andembodiment the transfer efficiency can be improved easily and theresulting reduction in the ink supply volume brings about the followingfive advantages.

(1) Reduced Bleeding and Beading

Bleeding and beading are both caused by contact between ink droplets.Thus a reduction in ink volume supplied to the intermediate transferbody results in reduced chances of contact between ink droplets.

(2) Reduction in Water Evaporation

For an improved transfer efficiency, enhancing an internal coalescentforce of ink is strongly desired. But since the ink for ink jet printinggenerally contains a large amount of water, the internal coalescentforce of ink is increased by removing the water. At this time, thesmaller the ink volume per unit surface area on the intermediatetransfer body, the more quickly and easily the water removal can bedone.

(3) Reduction in Dot Gain during Transfer

The greater the ink volume of each dot on the intermediate transferbody, the more likely it is to be flattened by the pressure during itstransfer and the larger the dot diameter will be, resulting in adegraded resolution. The reduced volume of ink, however, can preventthis.

(4) Load Reduction During Cleaning

As the volume of remaining ink on the surface of the intermediatetransfer body after the transfer decreases, the cleaning becomes easier.Particularly when different images are produced on different sheets, thesurface of the intermediate transfer body needs to be cleaned prior toeach image forming. In that case, this invention is advantageous.

(5) Improved Ink Utilization

The smaller the ink volume to be discarded by cleaning, the inkutilization improves, which in turn reduces the running cost and theamount of waste.

As described above, the combination of an intermediate transfer bodywith high cleaning performance and an ink jet printing device as adigital image printing means assures a high quality of printed imageseven if different images are produced on different sheets.

In addition, the ink jet printing system can use inks with a very smallsolid content and therefore has a capability of creating an imagewithout sacrificing a unique texture of a print medium or paper. To takeadvantage of this capability, the surface of the intermediate transferbody is made hydrophilic to allow aqueous ink and ink viscosityincreasing component to be applied in a thin layer without beingrepelled. This not only improves the quality of image but acceleratesthe water removal by spreading the ink thinly, which in turn results inan additional feature of being able to cope with a high-speed printing.

The surface with good releasability is excellent in terms of thetransfer efficiency. But such a surface is generally water repellentand, unless given some kind of surface treatment, repels liquid such asink, which renders the image holding and forming on this surfacedifficult. To deal with this problem, i.e., to make it possible to holdand form an ink image on a surface with high ink transfer efficiency isexactly why the surface modification through applying energy such asplasma treatment to the intermediate transfer body is done in thisinvention or embodiment. By modifying through energy application such asplasma treatment the surface of the intermediate transfer body havinghigh ink transfer efficiency and good releasability, it is possible tomake the intermediate transfer body surface suitable for holding inkwhile maintaining the inherently high ink transfer efficiency.

Further, applying an ink viscosity increasing component to theintermediate transfer body prior to the ink image formation can preventan image degradation even during a high-speed printing process where alarge volume of ink is applied in a short period of time. That is, byreducing the ink fluidity, unwanted phenomena such as ink beading andbleeding can be prevented if the ink droplets should come into contactwith each other. In a so-called “solid” printed area, it is difficult tokeep adjoining ink droplets from contacting each other however high thetransfer efficiency may be set. To the contrary, a water solution ofhigh molecular coagulant and metal ions, listed as examples of the inkviscosity increasing component, can instantly coagulate ink and lowerthe ink fluidity.

It is however not easy to uniformly coat the ink viscosity increasingcomponent over the surface with good releasability. If only the inkviscosity increasing component is applied, it is repelled on theintermediate transfer body surface. And if a wettability improving agentis to be added, a large volume of the agent will be required. This willmake the applied layer thick, offsetting the aforementioned advantage ofthe reduced volume of ink. It is therefore very effective to modify thesurface of the intermediate transfer body having good releasability byapplying energy such as plasma treatment to the surface and thereby makethe surface sufficiently hydrophilic before applying the ink viscosityincreasing component.

Further, even if the ink image formation is made possible by the surfacemodification, applying ink appropriately to the surface having goodreleasability is difficult as long as the surface contact method is usedfor ink application. The object of this invention is realized by usingas the image forming method an ink jet printing method which can applyink appropriately in a noncontact manner.

3. Example Embodiments

Next, some embodiments and examples for comparison will be explained indetail for each printing process. In the description that follows,“part” and “%” are expressed in mass terms unless otherwise specificallystated.

Embodiment 1

(a) Surface Modification of Transfer Body

As an intermediate transfer body this embodiment used an aluminum drumcoated with silicone rubber with a hardness of 40 degrees (KE12 ofShinetsu Kagaku make) to a thickness of 0.2 mm. First, the surface ofthe intermediate transfer body was modified under the followingconditions by using an atmospheric pressure plasma processor 3 (ST-7000of Keyence make).

Irradiation distance: 5 mm

Plasma mode: High

Processing rate: 100 mm/sec

(b) Application of Ink Viscosity Increasing Component

Next, the intermediate transfer body whose surface was modified wascoated with an ink viscosity increasing component using a roll coater.As the ink viscosity increasing component, a 10% by mass aluminumchloride hexahydrate solution in water was used.

(c) Forming of Image on Intermediate Transfer Body

Next, the ink jet printing unit (nozzle density: 1200 dpi (dots/inch),ejection volume: 4 pl, drive frequency: 8 kHz) was operated to form amirror-inverted character image of aqueous ink on the intermediatetransfer body. Here, the ink used has the following composition. Whenthe ink image was formed on the intermediate transfer body, it wasretained well and no beading resulted.

Pigment (Carbon black MCF 88 of Mitsubishi Kagaku make): 5 parts

Styrene/acrylic acid/ethyl acrylate copolymer (acid value: 240,weight-averaged molecular weight: 5,000): 1 part

Glycerin: 10 parts

Ethylene glycol: 5 parts

Surfactant (Acetylenol EH of Kawaken Fine Chemicals make): 1 part

Ion-exchange water: 78 parts

(d) Transfer

The intermediate transfer body, which was subjected to the above seriesof processes, and surface-coated print paper with little ink absorbingcapability (NPi coat paper of A-size of Nippon Paper make, 1000-sheetweight (ream weight; JIS P 0001): 40.5 kg) were brought into contactwith each other by the pressure roller to transfer the ink image to theprint paper. No beading was found on the image on the print paper andthe quality of the characters was good. After the image transfer, therewas almost no residual ink on the intermediate transfer body, so theintermediate transfer body was able to receive the next imageimmediately thereafter without a problem.

Embodiment 2

(a) Surface Modification of Transfer Body

As an intermediate transfer body this embodiment used an aluminum drumcoated with silicone rubber with a hardness of 60 degrees (KE30 ofShinetsu Kagaku make) to a thickness of 0.2 mm. First, the surface ofthe intermediate transfer body was modified under the followingconditions by using an atmospheric pressure plasma processor (PlasmaAtom Handy of Nippon Paint make).

Irradiation distance: Contact

Plasma mode: Standard

Processing rate: 10 mm/sec

(b) Application of Ink Viscosity Increasing Component

Next, 0.5% of fluorinated surfactant (Surflon S-141 of Seimi Chemicalmake) was added to a 10% by mass calcium chloride dihydrate solution inwater, and this solution was coated to the surface of the intermediatetransfer body whose surface was modified using the roll coater.

(c) Forming of Image on Intermediate Transfer Body

Next, the ink jet printing unit (nozzle density: 1200 dpi, ejectionvolume: 4 pl, drive frequency: 8 kHz) was operated to form amirror-inverted character image of four color inks on the intermediatetransfer body. Here, the ink used has the following composition. Whenthe ink image was formed on the intermediate transfer body, it wasretained well and neither beading nor bleeding resulted.

The following pigments: 8 parts

-   -   Black: Carbon black (MCF88 of Mitsubishi Kagaku make)    -   Cyan: Pigment Blue 15    -   Magenta: Pigment Red 7    -   Yellow: Pigment Yellow 74

Styrene/acrylic acid/ethyl acrylate copolymer (acid value: 240,weight-averaged molecular weight: 5,000): 1 part

Glycerin: 10 parts

Ethylene glycol: 5 parts

Surfactant (Acetylenol EH of Kawaken Fine Chemicals make): 1 part

Ion-exchange water: 78 parts

(d) Transfer

The fan installed between the ink jet printing unit and the pressureroller was operated to blow air against the ink image on the surface ofthe intermediate transfer body. Then, the intermediate transfer body andsurface-coated print paper with little ink absorbing capability (NPicoat paper of A-size of Nippon Paper make, 1000-sheet weight: 40.5 kg)were brought into contact with each other by the pressure roller totransfer the ink image to the print paper. Neither beading nor bleedingwas observed on the image on the print paper and the quality of thetransferred image was good.

Then, a small amount of residual ink on the intermediate transfer bodywas removed by placing a wet morton roller against the transfer body.

Embodiment 3

(a) Surface Modification of Transfer Body

As an intermediate transfer body this embodiment used an aluminum drumcoated with silicone rubber with a hardness of 80 degrees (KE24 ofShinetsu Kagaku make) to a thickness of 0.5 mm. First, the surface ofthe intermediate transfer body was modified under the followingconditions by using an atmospheric pressure plasma processor 3 (ST-7000of Keyence make).

Irradiation distance: 5 mm

Plasma mode: Metal

Processing rate: 75 mm/sec

(b) Application of Ink Viscosity Increasing Component

Next, fluorinated surfactant (Surflon S-141 of Seimi Chemical make) wasapplied to the surface of the intermediate transfer body whose surfacewas modified using the roll coater. Then, a 5% by mass high molecularcoagulant (C577S of Mitsui Cytec make) solution in water was appliedusing the roll coater.

(c) Forming of Image on Intermediate Transfer Body

Next, the ink jet printing unit (nozzle density: 1200 dpi, ejectionvolume: 4 pl, drive frequency: 8 kHz) was operated to form amirror-inverted character image of four color inks on the intermediatetransfer body. Here, the ink used has the following composition. Whenthe ink image was formed on the intermediate transfer body, it wasretained well and no beading resulted.

The following pigments: 4 parts

-   -   Black: C.I. Food Black 2    -   Cyan: C.I. Direct Blue 199    -   Magenta: C.I. Acid Red 289    -   Yellow: C.I. Acid Yellow 23

Glycerin: 10 parts

Ethylene glycol: 5 parts

Surfactant (Acetylenol EH of Kawaken Fine Chemicals make): 1 part

Ion-exchange water: 80 parts

(d) Transfer

The heat roller (surface temperature: 60° C.) held in contact with theback of the intermediate transfer body was activated to heat the inkimage on the intermediate transfer body, accelerating evaporation ofwater from the image. Then, the intermediate transfer body andsurface-coated print paper with little ink absorbing capability (NPicoat paper of A-size of Nippon Paper make, 1000-sheet weight: 40.5 kg)were brought into contact with each other by the pressure roller totransfer the ink image to the print paper. No beading was observed inthe image on the print paper and the quality of the transferred imagewas good.

Next, a small amount of residual ink on the intermediate transfer bodywas removed by placing a wet morton roller against the transfer body.

Embodiment 4

(a) Surface Modification of Transfer Body

In this embodiment, a polyester film 0.5 mm thick was undercoated with asilane coupling agent (KBM503 of Shinetsu Kagaku make) and then coatedwith silicone rubber with a hardness of 40 degrees (KE12 of ShinetsuKagaku make) to a thickness of 0.5 mm to form a surface layer of theintermediate transfer body. The intermediate transfer body surface layerwas modified under the following conditions using a parallel-plate typeplasma processor.

Irradiation distance: 5 mm

Gas flow: 100 sccm (standard cc/min)

Pressure: 0.08 torr (1.066 Pa)

Power: 1,200 W

Processing time: 30 sec

Next, this surface layer was wound on an aluminum drum to form anintermediate transfer body.

(b) Application of Ink Viscosity Increasing Component

Next, 1% of fluorinated surfactant (Surflon S-141 of Seimi Chemicalmake) was added to a 10% by mass calcium chloride dihydrate solution inwater, and this solution was coated to the surface of the intermediatetransfer body using the roll coater:.

(c) Forming of Image on Intermediate Transfer Body

Next, the ink jet printing unit (nozzle density: 1200 dpi, ejectionvolume: 4 pl, drive frequency: 10 kHz) was operated to form amirror-inverted character image of four color inks on the intermediatetransfer body which was coated with an ink viscosity increasingcomponent. The ink used is the same as the one used in Embodiment 2.When the ink image was formed on the intermediate transfer body, it wasretained well and neither beading nor bleeding resulted.

(d) Transfer

The fan installed between the ink jet printing unit and the pressureroller was operated to blow air against the ink image on the surface ofthe intermediate transfer body. Then, the intermediate transfer body andsurface-coated print paper with little ink absorbing capability (NPicoat paper of A-size of Nippon Paper make, 1000-sheet weight: 40.5 kg)were brought into contact with each other by the pressure roller totransfer the ink image to the print paper. Neither beading nor bleedingwas observed on the image on the print paper and the quality of thetransferred image was good.

Then, a small amount of residual ink on the intermediate transfer bodywas removed by placing a wet morton roller against the transfer body.

Embodiment 5

(a) Surface Modification of Transfer Body

In this embodiment, a polyester film 0.5 mm thick was undercoated with asilane coupling agent (KBM503 of Shinetsu Kagaku make) and then coatedwith silicone rubber with a hardness of 40 degrees (KE12 of ShinetsuKagaku make) to a thickness of 0.5 mm to form a surface layer of theintermediate transfer body. The intermediate transfer body surface layerwas modified under the following conditions using a parallel-plate typeplasma processor. The modified intermediate transfer body surface layerwas then mounted on a surface of an aluminum drum.

Irradiation distance: 5 mm

Gas flow: 100 sccm

Pressure: 0.08 torr (1.066 Pa)

Power: 1,200 W

Processing time: 30 sec

Further, the surface of the intermediate transfer body was modifiedunder the following conditions by using an atmospheric pressure plasmaprocessor (ST-7000 of Keyence make).

Irradiation distance: 5 mm

Plasma mode: Metal

Processing rate: 200 mm/sec

(b) Application of Ink Viscosity Increasing Component

Next, the intermediate transfer body whose surface was modified wascoated with an ink viscosity increasing component using a roll coater.As the ink viscosity increasing component, a 10% by mass aluminumchloride hexahydrate solution in water to which 1% of fluorinatedsurfactant (Surflon S-141 of Seimi Chemical make) was added was used.

(c) Forming of Image on Intermediate Transfer Body

Next, the ink jet printing unit (nozzle density: 1200 dpi, ejectionvolume: 4 pl, drive frequency: 12 kHz) was operated to form amirror-inverted character image of four color inks on the intermediatetransfer body which was coated with an ink viscosity increasingcomponent. The ink used is the same as the one used in Embodiment 2.When the ink image was formed on the intermediate transfer body, it wasretained well and neither beading nor bleeding resulted.

(d) Transfer

The fan installed between the ink jet printing unit and the pressureroller was operated to blow air against the ink image on the surface ofthe intermediate transfer body. Then, the intermediate transfer body andsurface-coated print paper with little ink absorbing capability (NPicoat paper of A-size of Nippon Paper make, 1000-sheet weight: 40.5 kg)were brought into contact with each other by the pressure roller totransfer the ink image to the print paper. Neither beading nor bleedingwas observed on the image on the print paper and the quality of thetransferred image was good.

Then, a small amount of residual ink on the intermediate transfer bodywas removed by placing a wet morton roller against the transfer body.

COMPARATIVE EXAMPLE 1

Image printing was done in the same way as in Embodiment 1, except thatthe intermediate transfer body was not subjected to the surfacemodification. As a result, the ink image on the intermediate transferbody was deformed and the image quality on a print medium after transferwas so poor that small characters were not readable.

COMPARATIVE EXAMPLE 2

Image printing was done in the same way as in Embodiment 5, except thatthe intermediate transfer body used a surface material of butyl rubberwith no releasing capability. As a result, the transfer rate wasdegraded and, to realize a good quality image obtained in Embodiment 5,about 1.5 times the ink volume spent in Embodiment 5 was required. Thetime needed to remove water by the air blowing operation from the imageforming to the transfer was 1.6 times what it took in Embodiment 5.Further, the image of this example had a slightly larger dot gain thanthat of Embodiment 5 and the resolution was degraded.

4. Example of Control System and Control Procedure

In constructing the image forming apparatus of FIG. 1 using variousunits employed in one of the above embodiments, the control system maybe formed as described below.

FIG. 2 shows an example configuration of a control system that may bebuilt for the image forming apparatus of FIG. 1. In the image formingapparatus generally denoted 100, reference number 101 represents a CPU,a main control unit for the entire system. Denoted 103 is a memoryincluding a ROM storing an operating system of CPU 101 and a RAM used totemporarily store a variety of data and to process image data and otherworks. Denoted 117 is an interface to send and receive data and commandsto and from an image source device 150, a source of image data which maytake a form of a host computer or others.

Designated 110 is a drive unit for driving the intermediate transferbody 1 in the processes (a) to (d). Reference number 115 represents atransport system for a print medium 10 and includes drive units for thepressure roller 11 and the fixing rollers 12. A bus line 120interconnects the aforementioned components and also an energyapplication device 3, which may take one of the forms described in theabove embodiments, an application device 4, an application device 5, anink jet printing unit 6, a water removal facilitating device 8, a heatroller 9 and a cleaning unit 13 and sends control signals from the CPU101. These components may be provided with status sensors so thatdetected signals are transmitted to the CPU 101 through the bus line120.

FIG. 3 shows a flow chart showing an example procedure of image formingprocess using the above control system.

When image data is received from the image source device 150 and theprinting of that image data is specified, predetermined image processingis performed on the image data so that the ink jet printing unit 6 canform an image (step S1). If the image data sent from the image sourcedevice is not mirror-inverted data, this image processing can includethe inversion processing.

When the ink jet printing unit 6 is ready to print, the intermediatetransfer body 1 is rotated (step S3), which is followed by the drivingof the energy application device 3 associated with the surfacemodification process (X) or (a) (.step S5; this can include the drivingof the application device 4 for applying a surfactant), followed by thedriving of the application device 5 associated with the process (b) forapplying the ink viscosity increasing component to the intermediatetransfer body 1 (step S6), followed by the driving of the ink jetprinting unit 6 associated with the image forming process (Y) or (c)(step S7), followed by the driving of the water removal facilitatingdevice 8, the heat roller 9, the print medium transport system 115 andthe cleaning unit 13, all associated with the process (Z) or (b) fortransferring the ink image onto the print medium. These components aresynchronously driven to ensure that the intermediate transfer bodysurface is modified for good image forming and that the position of theformed image and the transferred image position on the print medium arealigned correctly. If the ink jet printing unit 6 is of a serialprinting type, the image forming is done by alternating the main scan ofthe ink jet head and the rotation over a predetermined distance of theintermediate transfer body 1. When the processing of the specifiedamount of image data is completed, this procedure is exited.

While in the above procedure it is assumed that the surface modificationthrough energy application is performed at all times in the imageforming processing, it may be performed at an appropriate timing. Thatis, it may be performed prior to the image forming processing or itstiming may be managed based on the time spent and printed data volume,or it may be performed independently of the image forming processing bymonitoring a degradation of the intermediate transfer body surface.These may be combined as desired. Further, the time and degree ofsurface modification performed can also be set appropriately. Forexample, the surface modification may be performed for a few completerotations of the intermediate transfer body 1.

5. Others

It is not essential in this invention that all the processes (a)-(d) areexecuted during the image forming processing or that the device isequipped with all means to execute the associated processes. That is, ifthe intermediate transfer body which is surface-modified through energyapplication can keep its performance for a long period, this inventionalso includes an image forming method that performs processes (c) to (d)or processes (b) to (d) by using an intermediate transfer body which issurface-modified in advance by, for instance, the process (a) describedin connection with Embodiment 4, and an image forming apparatus equippedwith means to execute these processes. In other words, the onlyrequirement is that, prior to the image formation on the intermediatetransfer body, the intermediate transfer body be surface-modifiedproperly. So, the surface modifying process does not have to beperformed immediately before the application of the ink viscosityincreasing component to the intermediate transfer body or the formationof an ink image on the intermediate transfer body. Nor does the surfacemodifying means have to be provided in the image forming apparatus. Thatis, the intermediate transfer body may be removably mounted on amounting means in the image forming apparatus. Or a surface-modifiedintermediate transfer body may be mounted on the mounting means. Inaddition to these, this invention also includes a method of modifyingthe surface of the intermediate transfer body, suited for executing theimage forming method that performs the above process (c) or processes(b) and (c); the intermediate transfer body; and a method and a devicethat perform image forming by using the intermediate transfer body.

In this invention the application of the ink viscosity increasingcomponent in the above process (b) is not essential and may be omitted.To enhance the retainability of an ink image on the intermediatetransfer body, however, the process (b) should preferably be performed.The process (b), when executed, improves the retainability of an inkimage on the intermediate transfer body, which in turn provides a betterquality of a transferred ink image on a print medium than that obtainedwithout performing the process (b).

II. Second Embodiment

1. Characteristic Construction

Next, a second embodiment of this invention will be explained. Thisembodiment is characterized in that the intermediate transfer body has asurface made of a material containing fluorine compound or siliconecompound and that the surface is modified by subjecting it to plasmaprocessing and applying a surfactant to it. Following the surfacemodification, the same process as that of the first embodiment isperformed, i.e., forming an image on the intermediate transfer body andthen transferring it onto a print medium. Thus, an image formingapparatus can have almost the same construction as that shown in FIG. 1.The following description therefore centers on differences from thefirst embodiment.

The intermediate transfer body 1 of this example has a surface layer 2which is already subjected to a hydrophilic surface treatment throughplasma processing and application of a surfactant. An atmosphericpressure plasma processor 3 performs an additional surface modificationtreatment on the surface layer 2 at appropriate intervals along with thesurfactant application device 4 to maximize the surface modificationeffect according to the number of printed sheets.

To remove any excess surfactant supplied from the application device 4,a cleaning unit may be installed between the surfactant applicationdevice 4 and the ink viscosity increasing component application device5. If the interval of the additional surface modification treatment canbe set long, the cleaning unit 13 for cleaning the surface of theintermediate transfer body after the ink image transfer may also be usedto remove the excess surfactant. In that case, the device may be idledfor one process (which, in the example of FIG. 1, corresponds to onerotation of the intermediate transfer body 1).

As for the subsequent processes, this example has the similarconstruction to the first embodiment in that the ink viscosityincreasing component is applied from the application device 5, withother necessary units installed for executing the subsequent processes.

The image forming apparatus of this embodiment is characterized by asurface modification process in which the surface of the intermediatetransfer body 1 is modified through plasma processing and a surfactantapplication (hereinafter called a process (X′)). This image formingapparatus is similar to the first embodiment in that it includes meansto implement a process of forming an ink image on the intermediatetransfer body by the ink jet printing method and a process oftransferring the ink image formed on the intermediate transfer body 1onto a print medium, and that means to implement a process of applyingan ink; viscosity increasing component prior to the image forming canpreferably be provided. The process (X′) and the means to implement theprocess (X′) will be explained in detail by way of example.

The process (X′) is a process to modify the surface of the intermediatetransfer body by performing the plasma processing and the surfactantapplication operation on the surface whose material contains at least afluorine compound or silicone compound.

A preferred condition for the material of the surface layer 2 is that itcontain one of fluorine compound and silicone compound. These compoundshave an excellent releasability with respect to ink and thereforeprovide a high efficiency of transferring an ink image. The fluorinecompound and the silicone compound described here include fluorine oiland silicone oil which are an important material capable of enhancingthe transfer efficiency in particular. The releasability is as definedin the first embodiment. An example of the surface layer 2 is alsosimilar to the one explained in connection with the first embodiment.

The process (X′) modifies the surface layer 2 of the intermediatetransfer body 1 constructed as described above through plasma processingand surfactant application. The materials with an excellentreleasability, such as fluorine compound and silicon compound, generallyexhibit a low critical surface tension and thus repel liquids such asink and ink viscosity increasing component. Under this condition an inkimage cannot be formed on the intermediate transfer body. To cope withthis situation, the surface modification through plasma processing andsurfactant application is performed to minimize the ink repellingtendency. The plasma processing is generally performed at an atmosphericpressure or reduced pressure and either of the atmospheric and reducedpressure types can be used without a problem. The means that performsthe plasma processing at the atmospheric pressure is more advantageousbecause it can be installed in the image forming apparatus like theplasma processor 3 of FIG. 1 and perform additional surface modificationprocessing according the surface characteristic degradation the severityof which depends on the number of printed sheets. The plasma processingdescribed here includes a corona discharging that activates oxygen inthe atmosphere to create hydroxyl groups on the surface.

The surface modification is completed by applying a surfactant to thesurface following the plasma processing. With these processing, thesurface modification effect can be maintained for a long period of time.The surfactant used may include common surfactants, such as cationicsurfactant, anionic surfactant, non-ionic surfactant, amphotericsurfactant, fluorinated surfactant and silicone surfactant.

The means for applying the surfactant may preferably be ones thatperform a roll coating, a doctor coating and a spraying because thesecan apply the agent continuously. Depending on the construction of theimage forming apparatus, a dip coating which is a form of batchprocessing may also be employed.

This surface modification means not only performs the hydrophilicsurface treatment but has an effect of keeping from deteriorating, or ofimproving, the efficiency of transferring an ink image formed on theintermediate transfer body to a print medium at a later process.

The hydrophilic surface treatment that uses plasma processing at reducedpressure and a surfactant application is disclosed in Japanese PatentApplication Publication No. 61-036783 (1986) as being limited tosilicone rubber as an object of application. The present invention, onthe other hand, uses an intermediate transfer body which is not onlymade hydrophilic but also provided with an improved ink transferability.This invention therefore clearly differs from the above reference bothin the philosophy and in the limitations on a selected material and :anambient pressure for the plasma processing.

A mechanism of how these selected materials and selected surfacemodification means can produce a desirable effect has not yet been fullyunderstood. However, where fluorine or silicone oil component exists, itseems apparent that the hydrophilic surface treatment of this inventionrealizes a remarkable combination of the capability of making thesurface hydrophilic and the capability of maintaining or improving thetransferability and that, once the processing is performed, theseeffects tend to last for a long period. This suggests that, in additionto the generally known chemical action of the plasma treatment(introduction of hydrophilic groups on the surface) which makeshydrophilic at least a part of the rubber component, filler componentand oil component of the surface layer, a physical action (surfaceroughening) changes a part of a rubber structure to promote the oilcomponent movement on the surface. Further, since the surfactantapplication causes a surfactant to adsorb on the surface that was raisedto a high-energy state by the plasma treatment, hydrophilic groups areformed on the surface, making the surface a more stable hydrophilicsurface, with the result that the surface can exhibit the hydrophiliccharacteristic for a very long period. Actually, there is a tendencyobserved that there is a strong correlation between the hydrophilicproperty and the plasma deactivation time. That is, the shorter the timeinterval between the plasma treatment and the application of asurfactant, the greater the effect obtained.

The surface-modified intermediate transfer body generally may be removedof excess surfactant by a washing means before being supplied to thenext process. Applying a treatment such as heating before washing mayenhance hydrophilicity in a short period of time. In the image formingapparatus of FIG. 1, such a cleaning means may be installed between theapplication device 4 and the application device 5.

The surface modification may be performed on the intermediate transferbody 1 at all times or at predetermined intervals in an image formingapparatus that has a plasma processor 3 and a surfactant applicationdevice 4 as in the embodiment of FIG. 1. Or an intermediate transferbody with its surface already modified may be used in an image formingapparatus in which the plasma processor 3 and the surfactant applicationdevice 4 are not installed. Alternatively, they may be combined. Thatis, an intermediate transfer body with its surface modified in advanceis used, the plasma processor 3 and the surfactant application device 4are installed independently or in combination in the image formingapparatus, and then an additional surface modification treatment isperformed on the surface layer 2 at an appropriate interval according tothe number of printed sheets to maximize the surface modificationeffect.

In either case the technical features of this embodiment are summarizedinto two points: that an image forming performance is improved byperforming a hydrophilic surface treatment on the intermediate transferbody having fluorine or silicone compound that can offer a hightransferability; and that the image forming on the intermediate transferbody is done by an ink jet printing. Main effects produced by therealization of high transferability are a reduction in ink volumeapplied to the intermediate transfer body and an improved cleaningperformance. The above effects, the effects produced by the imageforming using the ink jet printing, and the effects produced by theoptional application of ink viscosity increasing component are similarto those obtained in the first embodiment.

The surface containing a fluorine compound or silicone compound, whichis basically employed in this embodiment, is generally water repellentand, if not treated, will repel liquids such as ink, making the formingand holding of an ink image on the surface difficult. The reason thatthis invention or embodiment performs the surface modification throughplasma treatment and surfactant application is to overcome this veryproblem, i.e., to allow an ink image to be formed and held on thesurface with a high ink transfer efficiency. By subjecting theintermediate transfer body having a surface containing a fluorine orsilicon compound with high ink transferability to the surfacemodification processing consisting of the plasma treatment andsurfactant application as described above, the surface of theintermediate transfer body can be made suited to ink holding whilemaintaining the inherently high ink transfer efficiency.

In this embodiment it is essential that the surfactant application isperformed after the plasma treatment. This is because the adsorption ofa surfactant on the surface, which was raised to a high energy state bythe plasma treatment, is considered to introduce hydrophilic groups onthe surface thereby making the hydrophilic surface more stable andmaintaining the hydrophilic property of the surface for a very longperiod.

In this respect, this embodiment differs from the first embodiment whichpermits an application of ink viscosity increasing component or, priorto this, an application of surfactant for improved wettability. That is,this embodiment is characterized in that the surfactant application islinked with the plasma treatment on the intermediate transfer body, withthe surfactant having a function of changing the surface characteristicof the intermediate transfer body. On the other hand, the firstembodiment is characterized in that the surfactant application is linkedwith, and is performed prior to, the process of applying ink and inkviscosity increasing component, with the surfactant having a function ofproviding an affinity between the intermediate transfer body and ink orink viscosity increasing component.

2. Example Embodiments

Next, example embodiments will be explained in detail for each printingprocess. In the following explanations, “part” and “%” are expressed inmass terms unless otherwise specifically stated.

Embodiment 6

(a) Surface Modification of Transfer Body

As an intermediate transfer body this embodiment used an aluminum drumcoated with silicone rubber with a hardness of 40 degrees (KE12 ofShinetsu Kagaku make) to a thickness of 0.2 mm. First, the surface ofthe intermediate transfer body was modified under the followingconditions by using an atmospheric pressure plasma processor 3 (ST-7000of Keyence make).

Irradiation distance: 5 mm

Plasma mode: High

Processing rate: 100 mm/sec

Next, the intermediate transfer body was immersed for 10 seconds in a 3%surfactant solution which was made by diluting a commercially availableneutral detergent composed of sodium alkylbenzenesulfonate with purewater. The drum was then washed with water and dried.

(b) Forming of Image on Intermediate Transfer Body

Next, a 5% by mass high molecular coagulant (C577S of Mitsui Cytec make)solution in water was applied to the surface of the intermediatetransfer body using the roll coater. Then, the ink jet printing unit(nozzle density: 1200 dpi (dots/inch, reference value), ejection volume:4 pl, drive frequency: 12 kHz) was operated to form a mirror-invertedcharacter image of aqueous inks on the intermediate transfer body. Theink used has the following composition. When the ink image was formed onthe intermediate transfer body, no beading resulted.

The following dyes: 4 parts

-   -   Black: C.I. Food Black 2

Glycerin: 10 parts

Diethylene glycol: 5 parts

Surfactant (Acetylenol EH of Kawaken Fine Chemicals make): 1 part

Ion-exchange water: 80 parts

(c) Transfer

Following the above processes, the intermediate transfer body andsurface-coated print paper with little ink absorbing capability (NPicoat paper of A-size of Nippon Paper make, 1000-sheet weight: 40.5 kg)were brought into contact with each other by the pressure roller totransfer the ink image to the print paper. No beading was observed onthe image on the print paper and the quality of the transferred imagewas good. There was almost no residual ink on the intermediate transferbody surface, which in the current state was able to receive the nextimage without causing any problem.

Embodiment 7

(a) Surface Modification of Transfer Body

As an intermediate transfer body this embodiment used an aluminum drumcoated with silicone rubber with a hardness of 60 degrees (KE30 ofShinetsu Kagaku make) to a thickness of 0.2 mm. First, the surface ofthe intermediate transfer body was modified under the followingconditions by using an atmospheric pressure plasma processor 3 (PlasmaAtom Handy of Nippon Paint make).

Irradiation distance: 1 mm

Plasma mode: Standard

Processing rate: 10 mm/sec

Next, the intermediate transfer body was coated for 10 seconds with aspray of a 1% surfactant solution which was made by diluting a siliconesurfactant (Silwet L-77 of Nippon Unicar make) with pure water. The drumwas then washed with water and dried.

(b) Forming of Image on Intermediate Transfer Body

Next, the surface of the intermediate transfer body was applied by aroll coater with a treatment liquid, which was made by adding 0.5%fluorinated surfactant (Surflon S-141 of Seimi Chemical make) to a 10%by mass calcium chloride dihydrate solution in water. Then, the ink jetprinting unit (nozzle density: 1200 dpi, ejection volume: 4 pl, drivefrequency: 10 kHz) was operated to form a mirror-inverted characterimage of 4 color inks on the intermediate transfer body. The inks usedhave the following compositions. When the ink image was formed on theintermediate transfer body, neither beading nor bleeding resulted.

The following pigments: 3 parts

-   -   Black: Carbon Black (MCF88 of Mitsubisi Kagaku make)    -   Cyan: Pigment Blue 15    -   Magenta: Pigment Red 7    -   Yellow: Pigment Yellow 74

Styrene/acrylic acid/ethyl acrylate copolymer (acid value: 240,weight-averaged molecular weight: 5,000): 1 part

Glycerin: 10 parts

Ethylene glycol: 5 parts

Surfactant (Acetylenol EH of Kawaken Fine Chemicals make): 1 part

Ion-exchange water: 80 parts

(c) Transfer

First, the fan installed between the ink jet printing unit and thepressure roller was operated to blow air against the ink image on theintermediate transfer body. Then, the intermediate transfer body andsurface-coated print paper with little ink absorbing capability (NPicoat paper of A-size of Nippon Paper make, 1000-sheet weight: 40.5 kg)were brought into contact with each other by the pressure roller totransfer the ink image to the print paper. Neither beading nor bleedingwas observed on the image on the print paper and the quality of thetransferred image was good.

Embodiment 8

In the following, the image printing method of this embodiment will bedescribed for each process.

(a) Surface Modification of Transfer Body

As a surface layer of an intermediate transfer body this embodiment usedan aluminum plate 0.2 mm thick, coated with a fluororubber (Aflas 150Cof Asahi Glass make) to a thickness of 0.5 mm. First, the surface of theintermediate transfer body was modified under the following conditionsby using an atmospheric pressure plasma processor (AT-T02 of SekisuiKagaku make).

Irradiation distance: 2 mm

Input voltage: 240 V

Frequency: 10 kHz

Introduced gas: Wet air

Processing time: 30 sec

The intermediate transfer body surface was then coated by a spongeroller with a 5% surfactant solution which was made by diluting acommercially available surfactant of alkyl sulfate ester with purewater. It was left standing for 60 seconds and then washed with waterand dried.

Then, the intermediate transfer body surface layer was wound around analuminum drum as a support to form an intermediate transfer body.

(b) Forming of Image on Intermediate Transfer Body

Next, a fluorinated surfactant (Surflon S-141 of Seimi Chemical make)was applied to the surface of the intermediate transfer body using aroll coater.

Next, a 10% by mass aluminum chloride hexahydrate solution in water wasapplied by a roll coater. Then, the ink jet printing unit (nozzledensity: 1200 dpi, ejection volume: 4 pl, drive frequency: 8 kHz) wasoperated to form a mirror-inverted character image of 4 color inks onthe intermediate transfer body. The inks used are the same as used inEmbodiment 2. When the ink image was formed on the intermediate transferbody, neither beading nor bleeding resulted.

(c) Transfer

First, the heat roller (surface temperature: 60° C.) installed incontact with the back of the intermediate transfer body was operated toaccelerate evaporation of water from the ink image on the intermediatetransfer body. Then, the intermediate transfer body and surface-coatedprint paper with little ink absorbing capability (NPi coat paper ofA-size of Nippon Paper make, 1000-sheet weight: 40.5 kg) were broughtinto contact with each other by the pressure roller to transfer the inkimage to the print paper. No beading was observed on the image on theprint paper and the quality of the transferred image was good.

Then, a small amount of residual ink on the intermediate transfer bodywas removed by placing a wet morton roller against the transfer body.The residual ink was easily removed.

Embodiment 9

(a) Surface Modification of Transfer Body

In this embodiment, as an intermediate transfer body a polyester film0.5 mm thick was undercoated with a silane coupling agent (KBM503 ofShinetsu Kagaku make) and then coated with fluorosilicone rubber with ahardness of 60 degrees (FE361-U of Shinetsu Kagaku make) to a thicknessof 0.2 mm to form a surface layer of the intermediate transfer body.This surface layer of the intermediate transfer body was modified underthe following conditions using a parallel-plate plasma processor.

Irradiation distance: 5 mm

Gas flow: 100 sccm (standard cc/min)

Pressure: 0.08 torr (1.066 Pa)

Power: 1,200 W

Processing time: 30 sec

Then, fluorinated surfactant (Surflon S-141 of Seimi Chemical make) wasdiluted with pure water to produce a 10% surfactant solution, which wasapplied to the surface layer of the intermediate transfer body using asponge roller. The surface layer was left standing for 6.0 seconds andthen washed with water and dried.

The surface layer was then wound on an aluminum drum as a support toform an intermediate transfer body.

(b) Forming of Image on Intermediate Transfer Body

The ink jet printing unit (nozzle density: 1200 dpi, ejection volume: 4pl, drive frequency: 5 kHz) was operated to form a mirror-invertedcharacter image of 4 color inks on the intermediate transfer body whosesurface was applied with an ink viscosity increasing component. The inksused are the same as used in Embodiment 6. When the ink image was formedon the intermediate transfer body, neither beading nor bleedingresulted.

(c) Transfer

The fan installed between the ink jet printing unit and the pressureroller was operated to blow air against the ink image on the surface ofthe intermediate transfer body. Then, the intermediate transfer body andsurface-coated print paper with little ink absorbing capability (NPicoat paper of A-size of Nippon Paper make, 1000-sheet weight: 40.5 kg)were brought into contact with each other by the pressure roller totransfer the ink image to the print paper. Neither beading nor bleedingwas observed on the image on the print paper and the quality of thetransferred image was good.

The intermediate transfer body of this embodiment exhibited a good imageforming capability even after six months of storage.

3. Examples of Control System and Control Procedure

When the image forming apparatus of FIG. 1 is constructed using unitsand components employed in the above Embodiment 4 to 6, a control systemsuch as shown in FIG. 2 may be used (the energy application device 3 ofFIG. 2 is an atmospheric pressure plasma processor that can take one ofthe forms of the above embodiments and the application device 4 is asurfactant application device).

FIG. 4 is a flow chart showing an example image forming procedure. Herethose steps that can be executed in a way similar to those shown in FIG.3 associated with the first embodiment are assigned like referencenumbers.

This procedure is characterized by step S15 that drives the atmosphericpressure plasma processor 3 and the surfactant application device 4during the surface modification process (X′).

FIG. 5 shows an example of the surface modification procedure, which,when initiated, causes the atmospheric pressure plasma processor 3 toperform plasma processing (step S31) and the application device 4 toapply a surfactant (step S33). The execution duration of this procedureor the degree of surface modification can be determined appropriately.For example, this processing may be set to be performed for a fewrotations of the intermediate transfer body 1.

4. Others

With the second embodiment, it is not essential to execute all theprocesses (a) to (c) during the image printing processing described inconnection with Embodiment 6-9 or to have all means in the image formingapparatus to execute these processes. Further, the surface: modifyingmeans constructed by the plasma processor 3 and the surfactantapplication device 4 does not have to be provided in the image formingapparatus. This invention is also characterized by an intermediatetransfer body surface modifying method suited to executing the imageforming method that performs the processes (b) and (c) associated withEmbodiments 6-9. The invention is also characterized by the intermediatetransfer body.

Further, in performing the surface modification processing, the plasmatreatment and the surfactant application do not have to be combined butthey may be chosen as necessary. For example, if, after execution ofboth processes, a satisfactory surface modifying effect can bemaintained by performing only one of the processes thereafter, it ispossible to select only one of them for execution.

As described above, this invention provides an image forming methodwhich has no limitation on the kind of print medium and can outputdifferent digital images on different pages. This invention can alsomakes it possible to produce a small number of printed copies with highquality and low cost even if the print medium is a glossy material.

1. An image forming method comprising the steps of: performingsurface-modifying processing on a surface of an intermediate transferbody by applying energy to the surface; forming an image on thesurface-modified intermediate transfer body by ejecting ink from an inkjet printing means; and transferring the image formed on theintermediate transfer body onto a print medium.
 2. An image formingmethod according to claim 1, wherein the surface of the intermediatetransfer body contains at least one of a fluorine compound and asilicone compound.
 3. An image forming method according to claim 1 or 2,wherein the surface of the intermediate transfer body is formed of anelastic material with a hardness of between 10 and 100 degrees.
 4. Animage forming method according to any one of claims 1 to 3, wherein thesurface-modifying processing through the application of energy is plasmaprocessing performed at an atmospheric pressure or reduced pressure. 5.An image forming method according to any one of claims 1 to 4, whereinthe surface-modifying processing through the application of energy isadditionally performed at an arbitrary interval.
 6. An image formingmethod according to any one of claims 1 to 5, further comprising a stepof applying a first liquid for increasing an ink viscosity prior toejecting ink onto the surface of the intermediate transfer body.
 7. Animage forming method according to claim 6, wherein the first liquid isan aqueous solution containing at least metal ions.
 8. An image formingmethod according to claim 6 or 7, further comprising a step of applyinga second liquid for improving a wettability of the surface of theintermediate transfer body prior to ejecting the first liquid to thesurface.
 9. An image forming method according to any one of claims 1 to8, further comprising a step of promoting a removal of water from theink on the intermediate transfer body prior to transferring the inkimage onto the print medium.
 10. An image forming method according toany one of claims 1 to 9, further comprising a step of cleaning thesurface of the intermediate transfer body at least after the transferstep or before the surface-modifying processing step.
 11. An imageforming method comprising the steps of: providing an intermediatetransfer body having a surface containing at least one of a fluorinecompound and a silicone compound, and being surface-modified throughplasma processing for modification of the surface; forming an image onthe intermediate transfer body by ejecting ink from an ink jet printingmeans; and transferring the image formed on the intermediate transferbody onto a print medium.
 12. An image forming apparatus comprising:means for mounting an intermediate transfer body being surface-modifiedthrough application of energy for modification of the surface; means forforming an image on the intermediate transfer body mounted on themounting means by ejecting ink from an ink jet printing means; and.means for transferring the image formed on the intermediate transferbody onto a print medium.
 13. An image forming apparatus comprising:means for mounting an intermediate transfer body having a surfacecontaining at least one of a fluorine compound and a silicone compound,and being surface-modified through plasma processing for modification ofthe surface; means for forming an image on the intermediate transferbody mounted on the mounting means by ejecting ink from an ink jetprinting means; and means for transferring the image formed on theintermediate transfer body onto a print medium.
 14. An image formingmethod using an intermediate transfer body being surface-modifiedthrough application of energy for modification of the surface, themethod comprising the steps of: applying a first liquid for increasingan ink viscosity to the intermediate transfer body; forming an image byejecting ink from an ink jet printing means onto the intermediatetransfer body already applied with the first liquid; and transferringthe image formed on the intermediate transfer body onto a print medium.15. An image forming apparatus method comprising the steps of: providingan intermediate transfer body having a surface containing at least oneof a fluorine compound and a silicone compound, and beingsurface-modified through plasma processing for modification of thesurface; applying a first liquid for increasing an ink viscosity to theintermediate transfer body; forming an image by ejecting ink from an inkjet printing means onto the intermediate transfer body already appliedwith the first liquid; and transferring the image formed on theintermediate transfer body onto a print medium.
 16. A surface-modifyingmethod of an intermediate transfer body comprising a step ofsurface-modifying through application of energy, the intermediatetransfer body being used for forming an image formed of ink onto thesurface, and for transferring the image formed on the surface onto aprint medium.
 17. A surface-modifying method of an intermediate transferbody comprising the steps of: providing an intermediate transfer bodyhaving a surface containing at least one of a fluorine compound and asilicone compound, and being used for forming an image formed of inkonto the surface, and for transferring the image formed on the surfaceonto a print medium, and; surface-modifying the provided intermediatetransfer body through application of energy for modification of thesurface.
 18. An intermediate transfer body being surface-modifiedthrough application of energy, and being used for forming an imageformed of ink onto the surface, and for transferring the image formed onthe surface onto a print medium.
 19. An intermediate transfer bodyhaving a surface containing at least one of a fluorine compound and asilicone compound, being surface-modified through plasma processing formodification of the surface, and being used for forming an image formedof ink onto the surface, and for transferring the image formed on thesurface onto a print medium.
 20. An image forming method comprising thesteps of: performing surface-modifying processing on a surface of anintermediate transfer body through plasma processing and surfactantapplication, the surface containing at least one of a fluorine compoundand a silicone compound; forming an image on the surface-modifiedintermediate transfer body by ejecting ink; and transferring the imageformed on the intermediate transfer body onto a print medium.
 21. Animage forming method comprising the steps of: providing an intermediatetransfer body having a surface containing at least one of a fluorinecompound and a silicone compound, and being surface-modified throughplasma processing and application of a surfactant for modification ofthe surface; forming an image on the surface-modified intermediatetransfer body by ejecting ink from an ink jet printing means; andtransferring the image formed on the intermediate transfer body onto aprint medium.
 22. An image forming apparatus using an intermediatetransfer body having a surface containing at least one of a fluorinecompound and a silicone compound, the apparatus comprising: means forsurface-modifying processing on the intermediate transfer body throughplasma processing and surfactant application, means for forming an imageon the surface-modified intermediate transfer body by ejecting ink; andmeans for transferring the image formed on the intermediate transferbody onto a print medium.
 23. An image forming apparatus comprising:means for mounting an intermediate transfer body having a surfacecontaining at least one of a fluorine compound and a silicone compound,and being surface-modified through plasma processing and surfactantapplication for modification of the surface; means for forming an imageon the intermediate transfer body mounted on the mounting means byejecting ink from an ink jet printing means; and means for transferringthe image formed on the intermediate transfer body onto a print medium.24. An image forming method comprising the steps of: subjecting asurface of an intermediate transfer body to plasma processing; applyinga liquid onto the intermediate transfer body after plasma processing,the liquid containing a surfactant for improving a wettability of thesurface of the intermediate transfer body; applying a reactant liquidfor reacting to ink onto the intermediate transfer body to which theliquid containing the surfactant was applied; forming an image on theintermediate transfer body after application of the reactant liquid byejecting ink from an ink jet printing means; and transferring the imageformed on the intermediate transfer body onto a print medium.
 25. Animage forming method comprising the steps of: providing an intermediatetransfer body having a surface,containing at least one of a fluorinecompound and a silicone compound, and being surface-modified throughplasma processing and application of a liquid containing a surfactantfor modification of the surface; applying a liquid onto the intermediatetransfer body after plasma processing, the liquid reducing the fluidityof an ink on the intermediate transfer body; forming an image on theintermediate transfer body after application of the liquid by ejectingink from an ink jet printing means; and transferring the image formed onthe intermediate transfer body onto a print medium.